Luminescent material



Patented Jan. 19, 1943 2,308,736 LUMINESCENT MATERIAL GuntherAschermann, Berlin-Zehlen-dorf, and

Hedwig Strubing, Berlin-Britz, Germany, assignors to General ElectricCompany, a corporation of New York No Drawing. Application June 11,1941, Serial No. 397,604. In Germany August 7, 1940 8 Claims.

The present invention relates to luminescent materials generally, andmore particularly the invention relates to luminescent silicates similarto those disclosed in the co-pending application Serial No; 356,115,filed September 9, 1940, which is assigned to the assignee of thepresent application.

The luminescent materials disclosed in the copending application aresilicates of aluminum, beryllium or magnesium, or mixtures thereof,activated with cerium sesquioxide. Such silicates emit blue andultraviolet light when irradiated by low pressure or high pressuremercury vapor lamps.

The object of the present invention is to provide luminescent silicatesof the above type which emit very strong red light under radiation fromluminous mercury vapor discharges. Another object of the invention is toprovide a method of manufacturing such luminescent silicates. Stillfurther objects and advantages of the invention will be apparent fromthe following detailed description thereof and from the appended claims.

We have discovered and demonstrated that luminescent silicates ofaluminum, beryllium and magnesium emitting strong red light undermercury vapor radiation are produced when these silicates containmanganese oxide as an activator in addition to cerium sesquioxide. Inview of the fact that an addition of manganese to a cerium sesquioxidefree silicate of aluminum, beryllium or magnesium does not produce amaterial capable of emitting light under excitation by mercury vaporradiation, the results attained by us are unexpected. The luminescentmaterials of the present invention are useful in conjunction withmercury vapor discharge lamps either alone or with other luminescentmaterials emitting green, blue or yellow light for the production ofdaylight or any other mixed light.

Preferably, the total weight of the two activators, manganese oxide andcerium sesquioxide, does not exceed 15% of the weight of the luminescentsilicate and the content of cerium sesquioxide is larger than thecontent of manganese oxide. The cerium and manganese are preferably in aratio of 10 to 1 up to 2 to 1, and particularly good results areobtained when these ingredients are in a ratio of 5 to 1. Aluminumsilicates containing 5% by weight of cerium sesquioxide and 1% by weightof manganese oxide emit a bright red light. A content of more than 2% byweight of manganese gives a gray color to the otherwise pure whitepowder, but

does not change the color of the light emitted thereby. The red lightemitted by the material deepens in color as the content of cerium andmanganese is increased.

The method of manufacturing the luminescent materials of the presentinvention is very simple. Pure aluminum oxide, beryllium oxide ormagnesium oxide, or, when desired, a mixture of two or all of thesematerials is mixed with. pure silicic acid in the ratio of 3 to 1 toproduce a metasilicate, or in a ratio of 3 to 2 to produce an vorthosilicate. It is not essential, however, that these stoichiometricratio-s be accurately maintained. Cerium and manganese are added asoxides, such as cerium dioxide (C602) and manganese dioxide (M1102), oras salts, such as cerous nitrate CE(NO3)3 and manganese chloride(MnClz). The batch containing the above ingredients is then thoroughlymixed. This is done preferably by grinding the batch in a wet state forseveral hours in a porcelain ball mill. The mixture is dried and heatedfor approximately one-half hour in a reducing atmosphere to atemperature of approximately 1200 to 1300 degrees C. A reducingatmosphere of pure hydrogen is very effective. After completion of theheating step, the material i pulverized and sifted and is then ready foruse.

When desired, melting substances such as chlorides or carbonates of thealkalies, are added to the mixture for facilitating manufacture, and inquantities up to about 10% by Weight. When such materials are used, thelight output of the material is increased.

The luminescent materials of the present in- Vention are useful inconjunction with low pressure mercury vapor discharge devices of thepositive column type, such as tubular fluorescent lamps and sign tubesnow in extensive commercial use. These devices contain a starting gas,such as argon, at a pressure of approximately 1 to 10 mm. and a quantityof mercury, the vapor of which is luminous during the operation of thedevice. Preferably, the particles of luminescent material are applied tothe inner surface of the enevlope in such devices, though such particlesmay be applied to the outer surface of the envelope or on a supportingsurface separated from the device when the envelope consists of materialpervious to the exciting radiation emitted by the luminous mercuryvapor. The luminescent material is also useful in conjunction with highpressure mercury vapor discharge devices of the positive column typehaving an envelope of material pervious to the exciting radiation of themercury vapor discharge. Due to the elevated temperature of the envelopeduring operation of such high pressure devices, the luminescent materialis supported in spaced relation to said envelope, for example, on theinner surface of a light transmitting jacket or sleeve about theenvelope of the device.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A luminescent silicate of at least one metal selected from the groupconsisting of aluminum,

beryllium and magnesium containing cerium content being in majorproportion and the manganese oxide content being in minor proportion ofthe total content of activators.

4. A luminescent silicate of at least one metal selected from the groupconsisting of aluminum, beryllium and magnesium containing up to about15% by weight of cerium sesquioxide and manganese oxide as activiators,the ratio of cerium sesquioxide to manganese oxide being between about10 to 1 and 2 to 1. V

5. A luminescentsilicate of at least one metal selected from the groupconsisting of aluminum, beryllium and magnesium containing about 5% byweight of cerium sesquioxide and 1% by weight of manganese oxide.

6. A luminescent aluminum silicate containing 5% by weight of ceriumsesquioxide and 1% r by weight of manganese oxide. 7

'7. The method of manufacturing, a luminescent silicate which comprisesthe steps of mixing pure silicic acid, a pure oxide of a material fromthe. 1

8. The method of manufacturing a luminescent silicate which comprisesthe steps of mixing pure silicic acid, a pure oxide of a material from"the group consisting of aluminuimberyllium and magnesium, an alkalicompound, a compound of,

cerium and a compound of manganese, and heating said mixture in areducing atmosphere to a temperature of approximately 1100 to 1300 C.

GUNTHER ASCHERMANN. HEDWIG STRUBING.

